Manchester United cannot be taken seriously as a contender to win the Champions League until they sign a player of the calibre of Cristiano Ronaldo or Lionel Messi, according to 2008 winner Rio Ferdinand. Jose Mourinho's side are already on the brink of qualification for the knockout stage of this season's competition after maintaining their 100% record by beating CSKA Moscow 4-1 on Wednesday (27 September).

Two goals from Romelu Lukaku, an Anthony Martial penalty and Henrikh Mkhitaryan's second-half effort was enough to see off their Russian opponents, a victory that Mourinho believes puts his team "almost" in the last 16. United are top of Group A with six points, three ahead of Basel and CSKA in the race for qualification.

United spent close to £150m (€171m) in the summer, bringing in Lukaku, Nemanja Matic and Victor Lindelof, but Ferdinand feels the club are still short of a "superstar" who can help them dominate Europe. Record signing Paul Pogba missed the game through injury, yet the ex-England international wants to see further additions.

"Power and speed has been brought into this Manchester United team but you need more than that to win the Champions League – you need a superstar in your team to be the go-to guy when things are tight," he told BT Sport, according to Goal.com. "If you look at the Real Madrid team that have won it in recent seasons they've had a Cristiano Ronaldo and lately Isco, or Barcelona had Lionel Messi and Neymar.

"You need a star player and Man United have got players that could become that, but we need to find out who that will be and if they can reach that level. Winning the trophies Man United did last season is good experience for this squad and with the age of the players there's plenty of potential there, but there are still steps to go."

Ronaldo and Messi are in the midsts of negotiating new contracts with Real and Barcelona respectively, though each deal has hit a stumbling block. Current Ballon d'Or holder Ronaldo wants a fresh deal worth €25m a year – similar to that of Messi or Paris Saint-Germain forward Neymar – though the La Liga and Champions League holders have rejected such demands, according to Marca.

Meanwhile, Messi – whose contract expires at the end of the season – has yet to sign his new Barca contract, despite his father having put pen to paper on the deal. President Josep Maria Bartomeu has attempted to downplay any fears the Argentina international, who is free to speak to clubs from overseas from January, will leave the Nou Camp – though the delay on the agreement is causing concern around the Catalan giants.

Lionel Messi and Cristiano Ronaldo
Messi and Ronaldo have between them scooped the latest nine world footballer of the year awards.Getty Images